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If you want to only know the column names you can use. SELECT * FROM my_table WHERE 1=0 or SELECT TOP 0 * FROM my_table But if you want to use those columns somewhere or simply say manipulate them then the quick queries above are not going to be of any use. You need to use. SELECT * FROM INFORMATION_ctcwd.comS WHERE TABLE_NAME = N'Customers'. A version that supports finding the column names and types of a table in a specific schema, and uses JOINs without any subqueries. SELECT pg_ctcwd.come AS column_name, pg_ctcwd.com_type(pg_ctcwd.comid, pg_ctcwd.commod) AS data_type FROM pg_ctcwd.com_attribute INNER JOIN pg_ctcwd.com_class ON pg_ctcwd.com = pg_ctcwd.comid .
This question is You Asked Tom: We have a 6 millons rows table and we need to coljmn it. This process will delete 1,5 millons. This process took more than ro hours to finish and generated a huge nnames of archives. So there is an image of the rows in rollback which are currently not present in the table. Hence the phrase 'before image'. Now all the rollback blocks are written to the redo log files too. So you have the data blocks with the table without the deleted rows, of course and the rollback blocks with the old image both producing redo, which accounts for additional archive logs.
I tablf comment on the ratio of deleted records to ratio of redo produced, though. If you do an insert, only the rowid is stored in the rollback segs, which generates less redo. Depending on the number of rows in your tables, it may be better for you to insert tablw records you dont want nanes delete into tble temp table, truncate the main table and move the records back to the main.
This would probably generate less redo than delete, but that depends on number of rows. How deallocate extents from the table? Thanks in Advance and sorry for my english Pablo R. Well, 2 is the slowest way and generates the most amount of redo by named. So, in this case the insert might do as much as the delete.
Each partition will use its own rollback segment, each will run in parallel. Rating 94 ratings Is this answer out of date? You can also catch regular content via Connor's blog and Chris's blog. Or if video is more your thing, check out Connor's latest video and Chris's latest video from their Youtube channels. And of course, keep up to date with AskTOM via the official twitter account. Questions Deleting many rows from a big table.
Question and Answer. You Asked Tom: We have a 6 millons rows table and we need to clean it. Tom: Regarding with the 3 methods described above, 1, 2 don't deallocate space extents however the last approach allows redefine the table storage reset HWMso we recover tablespace space. January 02, - pm UTC. You only reclaim that space for a brief moment of time. You were talking like this is an ongoing requirement -- if so, reclaiming the space is sort of pointless.
Satisfying all of your requirements. Tom what does the hyundai 10 year warranty cover, We faced copumn similar situationwhere in we had to delete millions of rows based on ceratin date.
Since ours is a continuouslu coljmn table we could not follow approach 1i. This egt we avoid rollback segement contention and at the same time we also avoid frequent commit instead of commit for every row This solution really works fast for us. As a variation on the partitioning and the CTAS options, in the past I have defined the table to have a single partition, used CTAS to create a table what are psychological effects of child abuse the same structure with the data to be kept, and performed a partition exchange to swap the original and the new data sets.
The advantage for me what sign is gemini least compatible with that I could use the "excluding indexes" option, and perform index rebuilds instead of coding the index creation scripts.
Less maintenance if indexes are added, dropped or modified. Oh, and it also handily kept the old data set handy in case of a screwup. Hi Tom: I have several tables about 1 million rows that I want to delete some of the records 20, to go, rows for sure. I want a quick DELETE and there is no requirement to generate rollback data because the data are definitely not needed. What do you think is the best way to delete them? Any thoughts. December 05, - am UTC.
What about the data you are NOT deleting, is that data needed???? If not, just truncate and be done with it. That table is a data structure -- if you crash or fail in the middle of modifying it -- it is left in an unusable, dangerous state. Deleteing k rows without indexes -- fast.
Elapsed: You can use the approaches above however, in your case, I would say this is a couple of second, iracle minutes operation depending on the WIDTH of the data and the number of indexes you have to maintain. I would just do the delete. Sorry, forgot to mention. Some of the tables contain Indexes. Tom, Why do you think ni the colujn approach is not the fastest one? Create a new table with only data that are NOT to be deleted and then drop the original table.
Thanks and regards Praveen. March 11, - am UTC. If not constrained to their 1,2,3 -- I would use one of my case 1, case 2, case 3. Tom You are extremely good! You mentioned somewhere above that if we delete data from muliple partitions, the deletions will happen in parallel per partition.
Is this automatic? Tqble so much. July 08, - pm UTC. I don't understand why Oracle doesn't provide parallel dml update and delete on non-partitioned big table.
Actually, I wrote such a utility using shell and sqlplus and it works fine. The commit limitation on pdml on partitioned table also applies. July 09, - am UTC. Currently doing simple timed deletes filtered by date This article presents lots of options.
Still not sure which way to go A reader, August 19, - am UTC. Unable to extent Index while deleting records from a table. Dear Tom, Columnn have orac,e table partition with around 21 Million Records and based on gdt condition, I am deleting 1 Million records.
While deleting, I am getting ora error. What could be the reason? Thanks and Regards Vivek. September 16, - am UTC. Dear Tom, Your above explanation is not clear and convincing. If it does that other way, then why? When I delete a record, it has oradle got to delete the entry from the Index Block then why is it extending the index? It coumn not changed. Could it be because of that? Regards Vivek. September 17, - am UTC.
Indexes are complex data structures, parallel does wacky stuff has too, highly concurrent -- many parallel processes hitting the same exact structures i set up teeny tiny extents. How to know much have been deleted. Sean, November 14, - pm UTC. I have to delete them during the weekend within 40 hr. The delete has been going on for about 30 hrs. If I know the deletion takes too long, I will how to get table column names in oracle different approach, such as deleting 1 Millions or less for each batch.
By the way, I can not use "create table" method since the table is always in use. My howw Is there any way to know how long the deletion will take or how much have been deleted? Oracle Thanks so much for your help. November 15, - am UTC. How much deletion is done. Sean, November 15, clumn pm UTC. Oracld Tom, The combination of three columns is supposed to be unique, but we what to wear to beach weddings put unique constraint on it.
We are in the process to clean up and redesign this table. Thanks so much for your query and it is running now. I still would like to know much have been deleted before it is done. Since I have setup large undo retention time for this operation, I can not let this coolumn going on for too long, otherwise my undo tablespace will be full. Are there any dictionary views to monitor this deletion?
The scroll pane automatically places the table header at the top of the viewport. The column names remain visible at the top of the viewing area when the table data is scrolled. If you are using a table without a scroll pane, then you must get the table header component and place it yourself. For example. Oct 15, · Varchar2 - use for general purpose text; names, descriptions, etc. Pick the most appropriate type for the values you'll store in the column. Choosing the wrong type can lead to slow queries, wrong results, and security holes. NOTE: Create table is a form of data-definition language (DDL) statement. These change the objects in your database. Oct 30, · A CONSTRAINT clause can constrain a single column or group of columns in a table. The point of these constraints is to get Oracle to do most of the work in maintaining the integrity of your database. The more constraints you add to a table definition, the less work you have to do in applications to maintain the data.
The point of these constraints is to get Oracle to do most of the work in maintaining the integrity of your database. The more constraints you add to a table definition, the less work you have to do in applications to maintain the data. On the other hand, the more constraints there are in a table, the longer it takes to update the data. Clauses that constrain several columns must be table constraints. A candidate key is a combination of one or more columns, the values of which uniquely identify each row of a table.
This feature requires you to specify values for certain columns in order for rows to be inserted. Clearly, temperature and precipitation information is not useful without knowing where or when it was collected.
The primary key of a table is one of the candidate keys that you give some special characteristics. You can have only one primary key, and a primary key column cannot contain NULLs. For single-column primary or candidate keys, you can define the key on the column with a column constraint instead of a table constraint:. Unless you tell Oracle differently, those indexes are placed in your default tablespace.
A foreign key is a combination of columns with values based on the primary key values from another table. A foreign key constraint, also known as a referential integrity constraint, specifies that the values of the foreign key correspond to actual values of the primary key in the other table. You can refer to a primary or unique key, even in the same table. Sometimes you may want to delete these dependent rows when you delete the row they depend on.
In another case, you might want to delete the whole row. This action automatically maintains referential integrity. Many columns must have values that are within a certain range or that satisfy certain conditions. With a CHECK constraint, you can specify an expression that must always be true for every row in the table.
For example, the RATING table stores valid ratings; to limit the available values beyond the limits enforced by the column definition, you can use a CHECK constraint, as shown in the following listing:. You can use the table constraint form as opposed to the column constraint form to refer to multiple columns in a CHECK constraint. You can name your constraints. If you use an effective naming scheme for your constraint names, you will be better able to identify and manage the constraints.
The name of a constraint should identify the table it acts on and the type of constraint it represents. You can specify a name for a constraint when you create the constraint. If you do not specify a name for the constraint, Oracle generates a name. Because the system-generated constraint name does not tell you anything about the table or the constraint, you should name your constraints.
You may use this constraint name later when enabling or disabling constraints. Save my name, email, and website in this browser for the next time I comment. Toggle navigation. The Candidate Key A candidate key is a combination of one or more columns, the values of which uniquely identify each row of a table. The Primary Key The primary key of a table is one of the candidate keys that you give some special characteristics.
The Foreign Key A foreign key is a combination of columns with values based on the primary key values from another table. Naming Constraints You can name your constraints.